Water dispersible granules (WDG's) are becoming increasingly important in the formulation of agricultural compositions because they are more safely handled and environmentally friendly. For example, chemical spills of WDG's are easily cleaned, no toxic solvents are present in the WDG formulation, and it is possible to package WDG's in water soluble packaging, thus reducing user exposure.
The typical processes for making WDG's are pan granulation, spray drying, fluid bed granulation, and mixing agglomeration. The choice of which process to use depends on several factors, including the physical and chemical properties of the active ingredient(s), environmental and safety aspects, and volume and packaging requirements.
Pan granulation produces compositions having good dispersibility and can be used for low-melt, active ingredients. The disadvantage of pan granulation is that the granules are often dusty, and the size distribution of the granule is difficult to control. Spray drying produces compositions in high volume and good dispersibility, however the bulk density of the product is usually low and it is difficult to spray dry low-melt, active ingredients. Fluid bed granulation has basically the same advantages/disadvantages as spray drying, while mixing agglomeration has similar advantages/disadvantages as pan granulation.
The inert components of a typical prior art WDG formulation include a wetting agent, a suspension agent, a disintegrating agent and a carrier. Some commonly used wetting agents are sodium dioctyl sulfosuccinate, sodium dodecylbenzyl sulfonate, sodium lauryl sulfonate. Suspension agents are usually high molecular weight ionic compounds such as alkyl naphthalene sulfonates or lignosulfonates. Salts, such as sodium chloride, sodium sesquicarbonate, and sodium acetate are often used as disintegrating aids. A wide range of carriers can be used. The most commonly used carriers are kaolin, diatomite, attapulgite, montmorillonite, bentonite and calcite.
Dinitroaniline herbicides, which are useful for the selective control of certain grasses and broadleaf weeds, have typically been formulated as emulsifiable concentrates, flowables, wettable powders or the like, which are diluted in a tank mix. These formulations, however, require handling, measuring and mixing prior to application. Attempts have been made, therefore, to prepare granular formulations which do not require the additional handling and attendant exposure before application to the soil.
Conventional dispersible granular compositions containing dinitroaniline herbicides have been difficult to prepare. Such herbicides, which are solid at room temperature but have melting points below 100.degree. C. have a tendency to cake, fuse or lump up when stored at or exposed to elevated temperatures, due to the excessive softening or partial melting of the herbicides. Moreover, they are often dusty and may cause staining.
In general, the above referred-to conventional dispersible granular compositions are prepared by blending and milling the appropriate amount of the selected dinitroaniline herbicide, a conventional inert carrier and one or more wetting and/or suspension agent(s), and optionally a disintegrating agent, followed by granulating the blend in the appropriate equipment using a binder solution as the granulating agent.
Efforts to produce stable granular formulations of such dinitroaniline herbicides without the drawbacks discussed above, and capable of uniform distribution, have been tried (see, e.g., U.S. Pat. No. 5,019,155). Efforts to prepare water dispersible granular compositions containing dinitroaniline herbicides with increased thermal stability have also been tried (see, e.g., U.S. Pat. No. 4,511,395). Efforts to improve dispersibility of a dinitroaniline-containing herbicidal composition in a solvent-free, WDG formulation, however, continue.
It is therefore an object of this invention to provide a solvent-free, water dispersible granular composition with improved dispersion properties.
It is also an object of this invention to provide a water dispersible granular composition comprising a novel dispersion enhancing agent.
It is another object of this invention to produce a non-dusting, non-staining, water dispersible granular composition having granules of substantially uniform size and density.
It is yet another object of this invention to provide storage stable water dispersible granular compositions.
It is a further object of this invention to provide a novel method for producing water dispersible granular compositions.
These and other objects of the invention will become more evident in the detailed description that follows.